$re = '/^([A-Za-z][A-Ha-hJ-Yj-y]?[0-9][A-Za-z0-9]? ?[0-9][A-Za-z]{2}|[Gg][Ii][Rr] ?0[Aa]{2})$/m';
$str = 'A1A 1AA
A1 1AA
A11 1AA
AA1 1AA
AA1A 1AA
AA11 1AA
A1A1AA
A11AA
A111AA
AA11AA
AA1A1AA
AA111AA
GIR 0AA
GIR0AA';
preg_match_all($re, $str, $matches, PREG_SET_ORDER, 0);
// Print the entire match result
var_dump($matches);
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for PHP, please visit: http://php.net/manual/en/ref.pcre.php